Few people would argue with the need for air bags on the inside of a car. But on the outside? The idea comes from TNO, a car company in the The Netherlands, where there are now 1.3 bicycles for every resident. Amsterdam alone is home to a half a million riders daily.

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In tests, TNO researchers found that when a car hits a bicycle, the rider usually ends up landing on the windshield, with the head and shoulder leading. So they developed an air bag that inflates on the outside of the car, between the bottom edge of the front windshield and the hood.

The car has a forward facing camera under the rear view mirror. Software picks out objects and decides whether it is a pedestrian or cyclist. When either one enters a "time critical" zone — meaning one that they might not have time to get out of the way or the car to brake, the system switches to 'alert' mode. Sensors in the car bumper detect the collision. Then the air bag deploys, covering the lower half of the windshield.

Safety for cyclists is a particularly salient issue in the Netherlands, where the number of bicycles in the country has grown to more than 18 million. And even though cycling in the Netherlands is relatively safe, there are still some 600 traffic deaths per year involving cyclists and pedestrians, and that number has remained relatively constant.